Automatic slack adjuster for brakes



Feb. 14, 1950 A. G. H. CARLBOM AUTOMATIC SLACK ADJUSTER FOR BRAKES Filedbee. 4, 1945 s Sheets-Sheet 1 Feb, 14, 1950 A. G. H. CARLBOM AUTOMATICSLACK ADJUSTER FOR BRAKES Filed Dec. 4, 1945 3 Sheets-Sheet 2 Feb. 14,1950 A. G. H. CARLBOM AUTOMATIC SLACK ADJUSTER FOR BRAKES 3 Sheets-Sheet3 Filed Dec. 4, 1945 application of the brake,

Patented Feb. 14, 1950 UNITED STATE 2,497,343 AUTOMATIC SLACK ADJUSTERFOR BRAKES Axel Georg Hjalmar assignor t0.- Svenska tor, Malmo, Sweden,

Carlbom, Malmo, Sweden, Aktiebolaget Bromsregulaa corporation of SwedenApplication December 4, 1945, Serial No. 632,720 8 Claims. (01. 188-202)This invention relates to automatic slack adjusters for brakes and moreparticularly to automatic slack adjusters of the kind comprising atwo-part brake rod one part of which is in the form of a screw-spindlehaving screw-threads of such a pitch as to make it non-self-locking, anoperating member movable axially in relation to the other rod part andadapted to be moved in relation thereto in one direction durinapplication and in the other direction during release of the brake, afirst nut screwed on the screw-spindle for coupling it to said other rodpart during and a second nut screwed on the screw-spindle for couplingit to the operating member during release of the brake.

Hereinafter, for the purpose of identification, said first and secondnuts will be called the coupling nut and the adjusting nut,respectively, and said other brake rod part which is usually tubularwill be called the tubular rod.

In automatic slack adjusters of the kind herein referred to, theadjusting nut has to be easily movable on the screw-spindle in onedirection (during application of the brake), whereas it must berelatively heavy to move on the screwspindle by the operating member inthe other direction in which latter the operating member moves inrelation to the tubular rod during release of the brake, so that acertain axial force has to be exerted on the adjusting nut for moving iton the screw-spindle in this direction. As may be gathered from the U.S. Patent No. 2,225,001 to Bert Henry Browall and from his pending U. S.Patent applicationSer. No. 431,173, filed February 16, 1942, now PatentNo. 2,312,384, granted -March 2, 1943, it has already been proposed toprovide a spring-pressed slip friction clutch between the adjusting nutand the operating member for determining the axial force which theoperating member will have to exert on the adjusting nut for moving iton the screw-spindle during release of the brake. In case also the axialforce exerted on the adjusting'nut by the operating member duringrelease of the brake depends on a spring (such as the spring 6 in the U.S. Patent No. 2,225,001), the separate spring which according to theaforesaid prior proposal is used for compressing the slip frictionclutch must necessarily be of such a selected power as will limit theforce required for moving the adjusting nut on the screw-'spindle to avalue satisfactorily less than the force which the operating memberunder the urgency of its springis ableto exert on the adjustingnut; or

2 rather the spring urging the operating member must be of such aselected power as issatisfactorily greater than the axial force requiredon the adjusting nut for moving it on the screwspindle and determined bythe power of the spring compressing the slip friction clutch providedbetween the adjusting nut and the operating member. Due to thepractically unavoidable tolerance in the manufacture of the two separatesprings mentioned, and further. due to the practical necessity of makingthem exchangeable in the manner that any-two springs out of twomanufactured series may be paired together, there must necessarily be arelatively widemargin between them, the import .of which is that thepower of the spring of the operating member must necessarily be selectedconsiderably in excess of the force required onthe adjusting nut formoving it on the screw-spindle in the direction in which the operatingmember moves in relation to the tubular rod during release of the brake.During application of the brake, the power of the spring of theoperating-member acts as a resistance to, and thus subtracts from, thebrake power, and for thisreason any power, of the spring of theoperating member in excess of the force required on the adjusting nutfor moving it on the screw-spindleduring release of the brake isundesirable. 1

One object of the invention is to provide an automatic slack adjuster ofthe kind referred to, in which spring power is used for urging theoperating member back into normal position during release of the brake,and in which the axial force required on the adjusting nut for movingiton the screw-spindle in the direction in which the operating membermoves in relation. to the tubular rod'during release-of the brakeiscontrolled automatically V. by said spring power for the purpose ofmaking the function of the slack adjuster practically insensible tochanges in said spring power.

Another object of the invention is to provide an automatic slackadjuster of the kind referred 'moving'it on the screw-spindle in thedirection :of the returning-movement of the-operating member in relationto the tubular rod during release of the brake. I

Still another object of the invention is to so combine said returnspring or springs of the operating member and said slip friction clutchthat the force required on the adjusting nut for moving it on the screwspindle in the direction of the movement of the operating member inrelation to the tubular rod during release of the brake will be adaptedor suited automatically to the power of said return spring or springs,wheree by the necessary margin between the power of said return springor springs and the said requisite force on the adjusting nut may bereduced to a minimum without hazarding the correct function of the slackadjuster.

These and further objects of the invention will be apparent from thefollowing detailed description of a preferred embodiment of theinvention illustrated by way of example on the accompanying drawings inwhich:

Fig. 1 is a longitudinal vertical section through the automatic slackadjuster,

Fig. 2 is a fractional plan view, partly in section, of the slackadjuster, drawn on a larger scale than Fig. 1.

Fig. 3 is a corresponding end view, partly in section, of the slackadjuster,

Fig. 4 is a fractional longitudinal section through the slack adjuster,drawn on a larger scale than Figs. 2 and 3,

, Fig. 5 is an end view of a detail as viewed from the right in Fig. 4,

Fig. 6 is an end view of another detail as viewed from the left in Fig.4,

Fig. '7 is an end view of still another detail as viewed from the leftin Fig. 4,

Fig. 8 is a diagrammatic longitudinal horizontal section through a bogieor truck for a railway car and illustrates, by way of example, one formof a brake rigging and the mounting of the slack adjuster therein. and

Fig. 9 is an end view. partly in section. of the mounting of the slackadjuster, drawn on a larger scale than Fig. 8.

In the drawings the invention is illustrated in a constructional formdevised for a conventional type of bogies or trucks for American railwayfreight cars. In this form the slack adjuster com ri es a two-part brakepush rod. but the invention is also app icable in cases where the slack.adjuster comprises a two-part brake pull rod.

In the form shown on the drawings the automatic slack adjuster comprisesa two-part brake push rod one part of which is in the form of anon-rotatable screw-spindle I having screwthreads of such a pitch as tomake it non-selflocking, whereas the other brake rod part is in the formof a non-rotatable tubular rod 2. The screw-spindle I is axiallyslidable in the tubu ar rod 2 under the control of a coupling nut 3screwed on the screw-spindle I for coupling it to the tubular rod 2 (soas to enable the two-part brake push rod formed by the screw-spindle Iand the tubular rod 2 to transmit brake power during application of thebrake), an operating member 4 movable axially in relation to thetubular' rod 2 and adapted to be moved in relation thereto in onedirection during application and in the other direction during releaseof the brake,

and an adjusting nut 5 screwed on the screw-spindle l for coupling it tothe operating member 4 during release of the brake. -The adiusting nut 5is easily movable on the screw-spindle I in one direction (duringapplication of the brake), but must necessarily be relatively heavyto'move on the screw-spindle I in the other direction, that is thedirection in which the adjusting nut 5 is moved by the operating member4 during release of the brake. Thus a certain force has to be exerted onthe adjusting nut 5 for moving it on the screw spindle I in the lastmentioned direction.

The ope-rating member 4 comprises a tube 6 having screwed onto itsopposite ends two sleeves land 8, respectively. The tube 6 is providedinternally at its ends with conical seats 6a and 6b for rcoaction withexternal conical surfaces on rings 9 and I0, respectively, which areinserted in the sleeves I and 8, respectively, and Which, when thesleeves" and 8 are screwed home on the ends of the tube .5, expand thetube ends into firm contact with the internal screw-threads of thesleeves I, 8 and :thus frictionally lock the sleeves 'I, 8 to the tubeends. The sleeve I is provided with an arm I'I ending in a fork I2provided with a transverse bolt I3. The sleeve 8 has an enlarged endportion forming a chamber I4 housing the adjusting nut 5. The chamber I4is provided with an end wall in the form of a ring I5 which is screwedinto the sleeve -8 and provided internally at its inner end with aconical seat Ilia for coaction with an external conical surface on aring I6 which is inserted in'the sleeve *8, so that, when screwing homethe ring I5, the ring I6 will -expand the inner end of the ring I5 intofirm contact with the internal screw threads for the same on the sleeve'8 and thus frictionally lock the ring in place.

On either side of a flange I! on the adjusting nut "5 there are tworings l8 and I 9, both of which are easily movable axially on theadjusting nut, and both of which are of a greater outer diameter thanthe flange H. In the flange I! there are a number of recesses 28, andthe ring I 8 is provided with a corresponding number of axialprojections 2i engaging into said recesses 20. The axial length of theprojections 21 is only slightly less than the axial dimension of theflange 11, but the radial dimension of the projections '2I is greaterthan the radial height of the flange I 1 Also the ring I9 is providedwith a (preferably greater) number of axial projections 22, which,however, are situated radially beyond the outer periphery'of the flangeIT. The spaces between the projections 22 are sufficiently wide topermit the projections 21 to engage into them, and the axial length ofthe projections 22 is less than that of the projections 21.

The sides of the rings I8, I 9 remote from those provided with theprojections 2| and 2 2, respectively, are ground to serve each as one ofthe races for the balls of two antifriction thrust ball bearings 23 and24, respectively. The other race for the balls of the antifrictionthrust bearing 23 is on a ring '25 guided in a recess 26 in the ring l5.Between'the ring and a flange 2! on the ring 15 there is inserted acompression spring 28 which by means of the antifriction thrust bearing23 normally holds the ring I8 in contact with the flange I1 and under arelatively light pressure. The other race for the balls of theantifriction thrust bearing 24 is on a ring 29 guided in a recess 30 inthe sleeve 8 and acted upon by means of a ring 3I axially movable on thesleeve 8 and provided with axial projections 32 :projecting into contactwith the ring 29 through apertures. 33 in the sleeve 8. Between the ring3| and a collar 34 slidably mounted on the tube 6 at the other endthereof (adjacent the sleeve 1) there are inserted two compressionsprings 35, 38 urging the ring 3| By this spring force, transmitted bythe ring 3|,

the projections 32, the ring 29 and the antifriction thrust bearing 24to the ring Hi, the latter is pressed firmly against the locking ring I6, the coacting surfaces of the two rings I6 and I9 preferably being ofa conical shape, as shown. To be exact, the force pressing the ring I9against the locking ring |6 equals the force of the two springs 35, 36less the counteracting force of the weak spring 28, which, however, isso small that it can be disregarded in this connection. By the force ofthe springs 35, 36 at the other ends thereof the collar 34 is pressedagainst the sleeve 1 screwed on the end of the tube 6, and as long asthe collar 34 abuts the sleeve 1 the force of the two springs 35, 36 isconfined within the operating member 4 and has no tendency to move it ineither direction. Preferably the two compression springs 35, 36 arecoiled in opposite dire'ctions so that they cannot possibly getentangled with each others coils.

The tubular rod 2 has an intermediate portion in the form of a tube 31encasing the two springs 35, 36 and the sleeve 8 and extending beyondthe latter. Thrusting against the end of the tube 31 beyond the sleeve 8there is a locking ring 38 held in place by a socket 39 fitted onto theend of the tube 31 and welded thereto at 40. The socket 39 extendsbeyond the locking ring 38, and in an internally screw threaded portionof the socket 39 outside of the locking ring 38 there is screwed atapering end socket 4| locked in place by the coaction of an internalconical surface 42 on the socket 4| with a corresponding externalconical surfaceon the locking ring 38. In the narrow outer end of thetapering end socket 4| there is screwed a protecting tube 43 whichcovers the part of the screw-spindle extending beyond the end socket 4|,and which thus protects this part of the screw-spindle against injuryand dirt. Also the locking of the tube 43 to the end socket 4| iseffected by means of a locking ring and an internal conical surface 45on the tube 43 for coaction with a corresponding external conicalsurface on the locking ring 44. When the tube 43 is screwed home, thering 44 is clamped between the tube 43 and a flange 46 in the end socket4|. The ring 44 may serve at the same time to guide the screw-spindle inrelation to the end socket 4|, similarly as the ring l may also serve toguide the screw-spindle in relation to the sleeve 8 of the operatingmember 4. I Screwed onto the other end of the tube 31 is a socket 41locked in place by means of a locking ring 48 with an external conicalsurface coacting with acorresponding internal conical surface on thetube 31. The inside of the socket 41 serves as a guide for the slidablecollar 34. Beyond the collar 34 the socket 41 has an end wall 49 merginginto a casing 50 encasing the sleeve 1 of the operating member 4 andprovided with a longitudinal slot through which the arm II on the sleeve1 projects. The casing 58 is closed by an end wall 52 beyond which itmerges into a jaw 53 for connecting the tubular rod 2 to a brake leverfrom which the tubular rod 2, during the braking operation, receivesbrake power in the form of a spushing force which will be transmitted bythe parts 56, 48, 41, 31,to the locking ring 38, and further by thecoupling nut 3 to the screwspindle i j The coupling nut 3 is housed inthe end socke 4| and comprises an internally screw-threaded 6.. sleeve54 having a flange 55, and a thrust ring 56 screwed onto the sleeve 54against the inner side of the flange 55. Preferably the sleeve 54 ismade of a. material, such as cast iron, having good sliding qualities,whereas the thrust ring 56 (as well as the locking ring 38) preferablyis made of a hard material, for instance hardened steel. The thrust ring56 has an edge 51 for contact with the locking ring 38.

bearing comprising a ring 58 on the sleeve 54, a series of balls 59- anda second ring 60 which is axially movable to some extent in relation tothe end socket 4| and guided in a recess 6| therein.

The ring 68 is urged by a spring 62 in the direction towards the flange55, so that this spring 62 normally holds the coupling nut 3 with itsedge 51 in contact with the locking ring 38. Thus the aforesaid pushingforce exerted on the tubular rod 2 during braking will be transmitted tothe coupling nut 3 in the form of an axial pressure of the locking ring38 on the contacting edge 51 of the coupling nut 3. The friction arisingbetween the locking ring 38 and the coupling nut 3 due to this pressurewill prevent rotation of the coupling nut 3 on the screw-spindle underthe action of the torque to which the coupling nut 3 will be subjectedas a result of said axial pressure on the same and the non-self-lockingcharacter of the screw-threads of the screw-spindle Thus thescrew-spindle will be coupled to the tubular rod 2 so as to partake inany movement thereof under the action of the aforesaid pushing forcethereon.

The outer end of the screw-spindle l projecting from the guard tube 43is provided with a jawv screwed onto this end portion and locked thereonby a pin 66, and which serves as a stop coacting with the adjusting nut5 to prevent the screwspindle I from being pulled out from the tubularrod 2 unintentionally.

Pivoted on a bolt 61 extending through a transverse bore in the base ofthe jaw 53 at one side thereof is a fork-shaped lever 68. The free endsof the two shanks of this lever 68-are located above and 'below thecasing 56 appertaining to the tubular rod 2, respectively, where theyare provided with cup-shaped seats 69, 18 for the one ends of two push:pins 1|, 12, respectively, the other ends of which project throughbores 13, 14, respectively, in the wall 49 and normally leave a smalldistance between them and the collar 34. Extending through the fork I2of the arm I and held in place relatively thereto by the bolt |3 is arod 15 provided in one end with a jaw 16 which preferably is adjustablyscrewed onto the rod 15, as shown at 11, and locked thereto in adjustedposition by means of a locking nut 18 and a spring washer 19. Welded tothe rod 15 behind the jaw 16 is an arm connected to the lever 68 bymeans of a pair of links 8| and two bolts 82 and 83. The rod 15 isprovided on its other end with an abutment 84 which similarly to the jaw16 is adjustably screwed onto the rod 15, as shown at85, and lockedthereto in adjusted position by means of a locking nut 88 and a springwasher 81. Thus the distance between the abutment 84 and the fork |2 ofthe arm I in normal position may be adjusted to any desired value.

On the outer' side of the flange 55 there is an antifriction thrustFigs. 8- and 9.: illustrate: an, example ofv the.

mounting: ofthe slack adjuster now described in; aa conventional-type ofbrakerigging for a.- coneventional type of bogieor truck for Americanrailway'freight cars. The bogie. or tnuck com-- prises two side'frames83: each provided with two jpurnalboxes 89, 99 for the two wheel axlesSI, 92;. respectively, and a. bolster 93 reposing on springs, (notshown) in the sideframes 8.8. and. serving to' support a car body.

From'acentral source; of, brake power on: the can. not. illustrated; onthe drawings, the brake power is, transmitted. to the bogie. or truck bymeans of a main brake pull rod. as having, a jaw 9.5-. conne'cted by abolt $5 to theupper end of a truclr.v live brake lever 9'5 which. bymeans. of a bolt 98- is connected to a. brake beam 99. Connected tothe... lower. end ofthelive brake lever 91: bysmeans of a bolt I80. isthe jaw 53 f the tubular'rod 2 of the slack adjuster. The jaw Shot thescrew-spindle I. of the slack adjuster is. connected by means of;a boltI Ill to a truck dead. brake lever Hi2 connected by means of a bolt.LOG-to a-brake. beam I64. The-upper end of. the

dead: brake lever Ill-2 is connected by means. of

a: bolt I85 toi aelink. H36 which in turn is. connected by means of. abolt It? to a bracket H353v on the: bolster 93. On the brake beams. 99I04 are the brakeshoesv IE9, IE1) which are suspended by breakhangers III, II-2-.- and which are [pressed against the wheels H3, H4 when thebrakes are applied.

For the actuation; of the operating member 4 of the slack adjuster thereis providedan actuatinglever Il-fi'pivoted onv a projecting pin IIS onthebrake beam 99 and; held in place thereon bya-nut. I. I (Fig. 9-). Theupper end of. the lever Hi isgconnected by means of a bolt. IIB to alink I 19,. connected by means of a bolt I29 to a bracket IZI on thebolster 93. Connected to the lower end of: the lever M5 by means ofatbolt I22 is a link I23 to which the jaw it of the actuating rodIiisconnected by means of a bolt I24. The ratio between the arms of theactuating lever H5 is the same as that between the arms: of the livebrakelever 9i", and preferably the lengths of the arms of the actuatinglever I I 5 are equal to those of the live brake lever 91.

The operation is as. follows. At released brake, the bolt 96 is inits,normal position shown in E'ig. 8,.and thebolt I is always is held inthe.position. shownv in. Fig. 8 by the link I I9 connected to the fixedbracket I2I As. the bolt 98 andthe pin H6. are both situated on. the.brake beam 99- and the distance between them thus isfixed,v the bolt I22will also beheld insuch a position. that the actuating rod I5 willtake afully determined normal position in relationv to the tubular: rod 2,which position is the one shown on .the drawings. In the thus.determined normal position of the leverSB the latter. permits the pushpins II, I2 to take a position inwhichthey leave the collar 34 free tothrust against the, end of, the, sleeve I;, and further leave a. smalldistance. between them and, the. collar 34, so that the, force of thesprings 35, 36 will be confined within the operating'; member i, and sothat the operating member 4"may move the said small distance. to theleft in Fig. 1, so that a corresponding distance may be obtained betweenthe adjusting nut 5' and the sleeve 54 of the coupling nut 3. Thus thecou plingynut" 3 is free to, thrust with itsedge 51 against the lockingring 38; and if the slack adjusten'when in this position, should besubjected toe compressive force; this-force will increase 8the-pressure; betweenthe locking ring 38 and the edge5'I and therebyprevent rotation of the cone plingnutt on the. screw-spindle i. Theimporticfthisis thattheslackadjuster will be lockedwhen in normal.position at. released brake,

When a braking operation is started, the'bolt 96 moves to theleft inFig. 8,.which results-in such-.arelative movement of the bolts, I00andIZZ that the actuating rod I5 will be pulled to. the

left. in Figs. 2 and 8 in relation to'the two-part brakepush rod 1, 2.Though it is to beobserved that whenv braking both the actuating rod I5and the two-part brake rod I, 2 will be moved, namely inopposite-directions, the relative movement between them is more easilyunderstood whenv lookedon as if the two-part brake rod I, 2 were,at-rest, and as if the actuating rod. were movingto the left in Figs. 2andi8.

When the actuating rod I5. is in normal position atreleased brake, theactuating arm 68 is in the above described position shown in Figs. 2 and8, in. which the abutment 84 and the arm H are at a certain distancefrom each other, corresponding to the desired value to which the slackadjuster is. to adjustthe brake. shoe clearances at released brake.During an application movement of the brake the actuating arm 68. isturned in the clockwise direction in Figs. 2 and 8, so that the pushpins II,v 12' will be pushed to the right and will, push theoperatingmember 4. tothe right until the sleeve 8 abuts the rear side of thelocking ring 38 (compare also Figs; I and 4). During this'movement theadjusting nut 5 will also have been moved with its right end intocontact with the coupling nut 3. and will have pushed the lattersomewhat to the right and there-by relieved the edge 51 from its C'OII-rtact with the locking ringcil. In this position of the parts, the forceof the spring 52 will be-transmitted by the intermediary of the ballbearing 58 and. the: coupling nut 3 to the adjusting nut 5 thus addingitself to the force of thespring 28 for diminishing the force pressingthe ring- I9 against the locking ring I8. It is to be noted, however,thatthe pressure of'the ring ISagainst the locking ring It is notmaterially affected by the. springs 28- and. IE2, as both these springsare. weak in comparison with the springs 35, 36; During. the continuedapplication movement of the brake after the operating member 4. cannotbe pushed any further to. the right, the push pins 'lI, I2 (see Figs. 1and 2) will push the col-v lar 34 slowly away from the sleeve l duringcompression of the springs 35, 35.

Should the, two-part brake rod I, 2 during this period. be subjected toa compressive force tend,- ing to push the screw-spindle I to. the left(as viewed in the drawings), in relation to the tubular rod. 2, thisforce. will tend to push, by the intermediary of the adjusting nut 5,the slipfriction clutch ring 59 away from the friction. ring It againstwhich. the slip friction clutch ring. I9 is. pressed. by the, force ofthe springs 35, 36* less the force. ofthe springs 23 and 62. Should. thecompressiveforce on the two-part brake push. rod I, 2 rise to a. valueapproximating. that of the force pressing. ring i9 against ring I6, thefrictional engagement between the two rings I6 and I9. will loosensufficientlyfor permitting the adjusting nut 5 to rotate on theantifriction thrust ball bearing 24 under the action of the torqueresulting iromthe'apushing force of thescrewspindle I and thenon-self-locking character of the screw-threads thereof- Thus thescrewspindle I will be pushed to the left in relation "stroke. movementof the two parts I and 2 of the two- 'to the tubular rod 2 (as viewed onthe drawings),

and during this relative movement of the two brake rod parts I and 2 thecoupling nut 3 thrusts against the adjusting nut 5 and Ipartakes in therotation thereof.

Such a compressive force as aforesaid arises in the two-part brake rodI, 2 during an application of the brake, if the brake shoe clearances atreleased brake are too small so that the brake shoes I99, I I during theapplication of the brake will come into contact with the wheels beforethe bolt 96 has travelled the distance corresponding to the desiredlength of the brake application The result of the described relativepart brake push rod is of course a shortening of the same, whereby thebrake shoe clearances will be correspondingly enlarged when the brake isreleased again.

However, when the bolt 96 has travelled a certain distance during theapplication of the brake, the abutment 84 has reached the arm II andbeagainst rotation and thus couple the screwspindle I to the tubular rod2, whereby further movement of the screw-spindle I into the tubular rod2 will be prevented. Thus the shortening of the two-part brake rod I, 2and the enlargement of the brake shoe clearances will be checked in agiven position of the bolt 95 during the brake application movement,sothat the brake application stroke attains its corresponding correctlength.

During the continued brake application movement the increasing brakepower will be transrnitted from the truck live brake lever 91 (Fig. 8)by the jaw 53, the tubular rod 2 and'the locking ring 38 to the couplingnut 3 andfrom the latter by the spindle I and its jaw 63 to the truckdead brake lever I92. Also after the brake shoes have been moved intocontact with the wheels, the bolt 95 will continue its movement as faras permitted by the unavoidable elastic deformation of the parts of thebrake rigging under the increasing brakingstress, and the operatingmember '4 will be moved correspondingly further to the left as viewed inthe drawings. But the adjusting nut is not compelled to partake in thisfurther movement of the operating member 4,

in that the adjusting nut 5, to begin with, quietly remains in itsposition on the spindle I during I said further movement of theoperating member I including the rings I9 and I6 compressed by thesprings 35, 35. Meanwhile, the projections 22 1 on the ring I9 movecorrespondingly to the left in relation to the engaging projections 2Ion the "ring I8, and the flange 21 approaches the ball bearing ring 25and compresses the spring 23.

the brake shoe clearances have their normal value.

At a braking operation, when the brake shoe clearances are too large,the brake shoes willnot "have reached into contact with the wheels when:

the abutment 84 reaches the arm I I, and thus the operating member Iwill have been moved correspondingly further to the left as viewed inthe drawings, before the brake shoes are in contact with the wheels.During the beginning of the movement of the operating member to the left(in relation to the tubular rod 2), the spring 28 will be compressed andthe projections 22 moved in relation to the engaging projections 2|, andthis time this movement will be sufiioient for disengaging theprojections 22 from the projections .2I, and for bringing the bottom ofthe recess 25 in contact with the ball bearing ring 25. On the continuedmovement of the operating member 4 to the left, the adjusting nut 5(which, as a result of the disengagement of the projections 22 and 2Ifrom one another, is made free to rotate) will be pushed by theintermediary of the antifriction ball bearing 23 to the left on thescrew-spindle I while rotating under the action of the torque dependingon the non-self-locking character of the screw-threads of thescrewspindle I.

When, during the release of the brake, the operating member 4 begins tomove back to the right under the" urgency of its return springs 35, 36,the adjusting nut 5 first remains in that position on the screw-spindleI to which it was moved during the preceding application of'the brake,and the projections 22 are moved into engagement again with theprojections 2|. It is possible, and even probable, however, that theadjusting nut 5 during the application of the brake was moved to such anangular position on the screw-spindle I that the projections 22 can notmove in directly between the projections 2| but will abut the endsthereof. In such a case the ring" I8 will be pushed to the right by theends of the projections 22 abutting the ends of the projections 2|, butas the projections 22 are of less. axial length than the projections 2|the latter will not be moved fully out of their engagement in therecesses 29 in the flange H but will remain in this engagement with theadjusting nut 5.

When, during the continued return movement of the operating member 4 tothe right, the ring I9 makes contact with the flange I'I, part of theforce of the compression springs 35, 36 (which until now with theirwhole force less relatively small force of the spring 28 have pressedthe slip friction clutch ring I9 against the conical surface on the ringIE) will tend to move the adthat is until those spaces between theprojections 22 which were nearest to the projections 2|, have been movedinto register with the latter. At this moment the spring 28 pushes thering I8 against the flange II so that the projections 22 will be engagedagain with the projections 2| and lock the adjusting nut 5 againstrotation in relation to the ring I9 which is held against rotation byits frictional contact with the ring. I5. Thus the screw-spindle I willbe compelled to partake in the further rightward movement of theadjust-- ing nut 5. I

' If the brake rigging is highly elastic, it may Q happen that a certainbraking stress remains 575* between the jaws 53 and 63ofthe two-partbrake saunas "i151 rod I 2' also after the operating member 51 has"arrived at the above described "position of its rightwardreturnvmovement. Should this happen, obviously the screw-spindle lcannot be moved through the coupling nut 3 untillthe brake releasemovement has proceededso farthat thelbraking stresshas ceased. Duringthis period, the force of thereturn springs 35, 3.5 will be distributedby the intermediary-of the ballbearing 24, on the contact surfaces ofthe ring I9 againstzthe ring I6 and against the flange I1 in such amanner that the pressure ofv the ring IS on the flange. .11, and therebythe torque exerted'on the adjusting "nutby the non-selflockingscrew-threads of the screw-spindle i, will increase and simultaneouslythe pressure of the ring vI9 zagainstltherring .Il6 -will ldecrease'asthev operating member '4 movies ato the right. When this increasingatorque be- I; comes equal to and. exceeds the :decreasing Aonak- -ingtorque depending on the rfriction between I the :coacting conicalsurfaces of the two 'members I 9 and 15,-thislast-mentioned ,sli-pfriction clutch slipszand thus permitstheadjustingnut 5 :to rotate onthe -.scr.ew-spindle I .(in which rotation the rings IS and I9 partake),and :thus to partake in the movement of the operating member l to --theright.

During the whole .of -this ;movement the :adjusting nut t5 will exert onthe screwspindle I the same axial force as thering I19 exerts .on theflange IFI.

When finally the brake =release.movement has proceedednsofar that the:braking stress ceases, the axial force exerted on the-screw-spindle Iby the adjusting inut 15 will .sufiice for taking the screw-spindle I.alongin the movement of the adjusting nut 5 to the right, in

that obviously the rotation of the adjusting :nut

bearing 59 offering to this movement' only the small resistanceretermined by the tendency of ,the relatively weak spring 62 tokeep'theledge51 on the thrust ring 55 in contact with the locking ring38. reached its normalorend positionjthe two-part brake push rod I, 2has been lengthened by'the outward axial movement of. thescrew-spirldled in relation to the tubular rod 2, and to an extentcorresponding to the amount by which thebrake -shoe clearances exceededtheir normal value. -During the continued brake clearance'rele'ase.movement, by which the abutment";,8'4 is moved away from the arm .I I,the two-part brake rod I,

,2 maintains its so adjusted length, soithatat fully released brake thebrakes'hoe clearances'arerestore dto their desired normal value. That isto .say thatthebrakewill be correctly adjusted "a'fter one'singleapplication andzrelease ofthesame.

axial force required on the adjusting -nut- 5 for thedisplacement'thereof on the screw'sp'in'dl'e I by the return springs 35,'36 "during the return movement of the operating member 4 =on therelease of the brakes, will be'c'ontrolledautomatically by the frictionclutch i6, !9 due to the compression thereof by the -'-return springs35, 36. This controlling effect of the utilization of the return springs"35, *36" also forthecoinpression of When the operating member .4 has Aswill be apparentfromthe above description, taken in connection with "thedrawings-the the slip frictiouaclutch it, I9 serves the purpose.

automatically, adapting or suiting ;the ,force required on the adjustingnut 5 for-the displacement thereof on thescrew spindle I during thereturn movement of the operating member 4 to the forceavailable fromthereturn springs 35, 36 for eifecting this displacement-1 of the adjustinging nut 5 for moving it on the screw spindle. I dur- .ing thereturnmovement of the operatingmember4lcan be kept small without hazardingthede- :sired ableness of the return springs 3.5, 36 to effect adisplacement of the adjusting nut 5 on the screw spindle I. The forcewhich during the return movement of the operating member l istransmitted as apushingforce onto the spindle ;I by the adjusting nut 5,may be called the adjusting force of the slack adjuster and maybevariedto suit different'demandsby varying the construction (chiefly thediameter and the conicity of the coacting friction surfaces) of theslipfrictioncl-utch I6, i I9.

What I claim and desire to secure by Letters Patent is:

,;1. In an automaticislack adjuster for brakes on? the characterdescribed, the combination comgprisinga two-part .bra-ke red one part'ofwhich is inthes-form of a tubular rodand the other partof which in theform ofa non-self-locking screw-spindle axially movable in the tubularrod,

(and means-for controlling therelative move- .ments of the screw-spindleand thetubular rod,

comprising-a coupling nut-screwed on the screwspindle and housed in thetubular rod for coupling the screw-spindleto the tubular rod duringapplication oftherbrakefa tubular operating member I housed the tubularrod and adapted .to be moved axially in relation thereto in onedirection during application of the brake, spring means forreturning theoperating member in the other direction in relation to the tubular rodduring release of the brake, actuating means for compressing said returnspring means during application of the brake, an adjustingnut screwed onthe screw-spindle-and housed in'the-tubular operating member forcoupling thescrew-spindle to the tubular operating member during releaseof the brake, and a slip friction clutch provided between the adjustingnut andthe tubular operating member and compressed by said return springmeans for controlling the axial force re- ,quired on the adjustingnut'ior moving it on the screw spindle bysaid return spring means duringthe return movement of the operating member.

,2. In an automatic slack adjuster as claimed in claim 1, the additionalfeature that the slip friction clutch provided between the adjusting nutand the operating member comprises a friction ring. disengageablycoupled to the adjusting nut and coacting both with a thrust surface onthe adjusting nut and .a friction surface on the operating-member andpressed against these surfaces by the return spring means by theintermediary of an I antifriction thrust bearing.

'3. In an automatic slack adjuster for brakes of. the characterdescribed, the combination comprising a two-part brake push rod one part.Of

*whichzis in the iormlof a tubular rod having a :jaweateone end-and the:other part of-whichnis II ain the form of "a -non-selflockingscrew-spindle 13 movable axially in the tubular rod and projectingtherefrom at the other end thereof, and means for controlling therelative movements of the screw-spindle and the tubular rod, comprisinga coupling nut housed in the tubular rod at said other end thereof andscrewed on the screwspindle for coupling it to the tubular rod duringapplication of the brake, a tubular operating member housed in thetubular rod and adapted to be moved axially in relation thereto in onedirection during application of the brake, and to return into a normalposition during release of the brake, a collar movable axially on theoperating member and guided in the tubular rod near the jaw end thereof,an abutment on the operating member near one end thereof for limitingthe axial movement of said collar in relation to the operating member inthe direction towards the jaw end of the tubular rod, an adjusting nutscrewed on the screw-spindle inside of the coupling nut and housed inthe adjacent other end of the tubular operating member for coupling thescrew-spindle to the operating member during release of the brake, aslip friction clutch provided between the adjusting nut and theoperating member and comprising a clutch ring disengageably coupled tothe adjusting nut and coacting with a thrust surface on the adjustingnut and with a friction surface on the operating member, a number ofcoiled compression springs disposed around the operating member andencased in the tubular rod and acting between said collar on theoperating member and said clutch ring so as to urge the latter againstsaid thrust and friction surfaces on the adjusting nut and the operatingmember, respectively, an antifriction thrust bearing disposed betweensaid springs and said clutch ring, an abutment on the tubular rod forlimiting the axial movecollar on the operating member for compressingsaid springs during application of the brake, so

that the operating member, during release of the brake, will return intothe normal position under the urgency of said compressed springs and inthe direction towards the coupling nut, while 1 said clutch ring beingpressed against said fric- 1 tion surface on the operating member bypart of the force of said compressed springs.

4. In an automatic slack adjuster as claimed; in claim 3, the additionalfeature that said actuating means comprises a fork-shaped lever endportion of the tubular operating member is enlarged to form a chamberfor the adjusting nut and is guided in the tubular rod, and that thepressure of the return springs is transmitted onto the slip frictionclutch ring on the adjusting nut bytfimeans of a ring slidably mountedon the operating member and provided with axial projections projectinginto said chamber through apertures in a wall thereof, and saidantifriction thrust bearing disposed between said projections and theslip friction clutch ring in said chamber. 7. In an automatic slackadjuster for brakes of the character described, the combinationcomprising a two-part brake rod one part of which is in the form of anon-self-locking screw-spindle an operating member movable axially inrelation to the other rod part and adapted to be moved in relationthereto in one direction during application of the brake, return springmeans for returning said operating member in the other adjacent the jawend thereof, axially movable push pins provided between this fork-shapedl lever and the movable collar on the operatin member and guided inbores in the tubular rod, and means operable by brake applicationmovement for turning said lever for compressing the return springs ofthe operating member durin application of the brake.

5. In an automatic slack adjuster as claimed in claim 3, the additionalfeature that said clutch ring is disengageably coupled to the adjustingnut by said clutch ring and a second springpressed ring being mountedslldably on the adjusting nut on either side of a recessed radial flangethereon, said second ring having axial projections engaged in therecesses of said radial flange and extended radially beyond the latter,and said clutch ring having axial projections disposed radially beyondthe outer periphery of said straddling the tubular rod and pivotedthereto direction in relation to said other rod part during release ofthe brake, a coupling nut screwed on the screw-spindle for coupling itto said other rod part during application of the brake, an adjusting nutscrewed on the screw-spindle for coupling it to the operating memberduring release of the brake, and a spring-pressed slip friction clutchprovided between the adjusting nut and the operating member andcompressed by part of the force of said return spring means forautomatically suiting the axial force required on the adjusting nut formoving it on the screw spindle by said return spring means during thereturn movement of the operating memberto the actual power of saidreturn spring means.

8. In an'automatic slack adjuster, for brakes of the characterdescribed, the combination comprising a two-part brake rod one part ofwhich is in the form of a non-self-locking screw-spindle, an operatingmember movable axially in relation to the other rod part and adapted tobe moved in relation thereto in One direction during application of thebrake, return spring means for returning said operating member in theother direction in relation to said other rod part during release of thebrake, a coupling-nut screwed on the screw-spindle for coupling it tosaid other rod part during application of the brake, an adjusting nutscrewed on the screw-spindle for coupling it to the operating member'iduring release of the brake, a slip friction clutch, provided betweenthe adjusting nut and the operating member, and means compressing saidslip friction clutch by force derived from said return spring REFERENCESCITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,270,501 Browall Jan. 20, 19422312.384 Browall Mar. 2, 1943

